It is generally known in the art to interconnect at least two different elements with a member such as a screw. For example, in medical procedures, a bone plate may be affixed to a fractured or broken bone using a screw which passes through the bone plate and thoroughly engages the substrate bone. In other medical applications, two portions, of fractured bone may be joined together by a screw. The screw generally includes a head portion, which allows a tool to engage the screw, and an integral shank portion, which has threads for engaging the substrate bone. The tool to engage the head portion may be any appropriate tool which can apply enough torque between the tool and the screw to thread it into the substrate.
With these commonly known systems, however, the entire screw is formed of a single material. This single material may be a material that is bio-absorbable. Therefore, after a period of time, the screw will resorb into the body into which it is implanted. Other screws may be formed of materials which are not bio-resorbable and remain permanently affixed within the body into which they are implanted. A bio-resorbable screw, after it has been resorbed, applies no fixation force to an implanted portion or to the bone into which it was implanted. On the other hand, a screw which is formed of a non-resorbable material remains permanently within the bone and may protrude undesirably from the bone into which it is affixed.
It is also known to provide a cannulated screw which includes a cannula through the screw. The cannula in the screw allows it to be guided into the implantation site using a guide system such as a wire. Therefore, the physician, while implanting the screw, does not need to have a clear view of the entire surgical area, but rather may use the wire to guide the screw into place.
It has become desirable to provide a screw which is modular. A modular screw may include a bio-resorbable and a non-bioresorbable portion to be implanted at a single location. Therefore, a non-resorbable portion may always be permanently affixed within the body to provide a fixation in the substrate. While the resorbable portion is resorbed into the body, thereby removing any protrusions which may not be desirable.
The insertion of such a modular screw can be particularly difficult. In particular, a modular screw may include a modular head which is inserted separate from the modular shank portion of the modular screw. Therefore, an instrument to engage such a modular screw requires unique and new characteristics to engage and insert the modular screw. If the modular screw is large enough, protrusions or indentations may be included on the modular screw which may be engaged by an instrument to insert and remove the modular screw. If the modular screw is particularly small, however, there may not be space to form such indentations or protrusions. Therefore, it is desirable to provide an instrument which can insert and remove a modular screw which is small and does not allow for the inclusion of protrusions or detents to be engaged by the instrument.